Borehole casing centraliser

ABSTRACT

A centralised segment ( 1 ) comprising a first collar portion ( 3 ), a second collar portion ( 5 ), and bows ( 7 ) extending between the first collar portion ( 3 ) and the second collar portion ( 5 ). First connectors ( 9 ) are provided at first locations of the first collar portion ( 3 ) and the second collar portion ( 5 ), respectively. Second connectors ( 11 ) are provided at second locations of the first collar portion ( 3 ) and the second collar portion ( 5 ), respectively. The first connectors ( 9 ) are engageable with the second connectors ( 11 ) of the same or another centraliser segment ( 1 ). In this way, one or more centraliser segments ( 1 ) are connectable together to form a centraliser around a borehole casing.

FIELD OF THE INVENTION

[0001] The present invention relates to a centraliser segment and a centraliser formed of one or more centraliser segments.

[0002] The centraliser may be used to centralise a borehole casing. Such borehole casings may be used, for example, in water wells, oil wells and gas wells.

DISCLOSURE OF THE INVENTION

[0003] In accordance with one aspect of the present invention, there is provided a centraliser segment comprising a first collar portion, a second collar portion, bow means extending between said first collar portion and said second collar portion, first connection means provided at first locations of said first collar portion and said second collar portion, respectively, second connection means provided at second locations of said first collar portion and said second collar portion, respectively, wherein said first connection means are engagable with said second connection means of the same or another centraliser segment such that one or more said centraliser segments are connectable together to form a centraliser around a borehole casing.

[0004] Preferably, said first and second connection means allow the relative positional engagement between said first and second connection means to be selected.

[0005] Preferably, said first connection means comprises teeth provided on said first and second collar portions on a first face of said centraliser segment and said second connection means comprises pawl means provided on said first and second collar portions on a second face of said centraliser segment.

[0006] Preferably said second connection means further comprises guide means for receiving first and second collar portions of a said centraliser segment.

[0007] Preferably, said first and second collar portions are provided with lug members on a face of said centraliser segment that, in use, faces away from the borehole casing.

[0008] The lug members can be used to tighten the centraliser segment around the borehole casing.

[0009] Preferably, said bow means is flexibly resilient.

[0010] Preferably, said bow means is curved in the direction between said first and second collar portions.

[0011] Preferably, said bow means extends between said first and second collar portions intermediate the locations of said first and second connection means.

[0012] Preferably, agitation promoting means is provided on said centraliser segment to promote agitation of grout injected into a borehole.

[0013] Preferably, said agitation promoting means comprise rib members provided on said bow means.

[0014] Preferably, said rib members are provided on a face of said centraliser segment that, in use, faces the borehole casing.

[0015] Preferably, at least one of said rib members is provided with at least one enlarged portion.

[0016] Preferably, said bow means comprises at least two strap members extending between said first and second collar portions.

[0017] Preferably, said first and second collar portions are substantially parallel.

[0018] Preferably, said first and second collar portions are provided as strap members.

[0019] Preferably, said centraliser segment is made of a corrosion resistant material.

[0020] In accordance with a second aspect of the present invention, there is provided a centraliser for a borehole casing comprising a centraliser segment, as hereinbefore described, connected together via said first and second connection means around a borehole casing.

[0021] The centraliser may comprise at least two centraliser segments connected together via said first and second connection means around a borehole casing

[0022] In accordance with a third aspect of the present invention, there is provided a centraliser for a borehole casing comprising at least two centraliser segments, as hereinbefore described, connected together via said first and second connection means around a borehole casing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0024]FIG. 1 is a first perspective view of an embodiment of a centraliser segment in accordance with one aspect of the present invention;

[0025]FIG. 2 is a second perspective view of the centraliser segment shown in FIG. 1;

[0026]FIG. 3 is a detailed view of a second connector of the centraliser segment shown in FIG. 2;

[0027]FIG. 4 is a first plan view of the centraliser segment as shown in FIG. 1;

[0028]FIG. 5 is an end view of the centraliser segment shown in FIG. 4;

[0029]FIG. 6 is a second plan view of the centraliser segment as shown in FIG. 2;

[0030]FIG. 7 is an end view of the centraliser segment shown in FIG. 6;

[0031]FIG. 8 is a side view of the centraliser segment shown in FIG. 6;

[0032]FIG. 9 is a perspective view of two centraliser segments joined together to form a centraliser around a borehole casing; and

[0033]FIG. 10 is a cross sectional view of a borehole having a borehole casing therein with a centraliser located thereon.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

[0034] In a first embodiment of a centraliser according to the present invention, two or more centraliser segments are connected together to form the centraliser around a borehole casing. An embodiment of a centraliser segment that can be used to form such a centraliser and the centraliser formed thereby is described herein in further detail with reference to FIGS. 1-10 of the drawings.

[0035] In a second embodiment of a centraliser according to the present inventions a single centraliser segment is connected together, i.e. connected to itself, to form the centraliser around a borehole casing.

[0036] The first embodiment of the centraliser is used with borehole casings having medium to large diameters, whilst the centraliser of the second embodiment is used with borehole casings having small diameters. The centraliser segment used to form a centraliser according to the second embodiment is similar to the centraliser segment used to form a centraliser according to the first embodiment except that it is smaller in size since it is used with borehole casings having small diameters.

[0037] The present invention will now be further described with reference to FIGS. 1-10 of the accompanying drawings.

[0038] In FIGS. 1-8, there is shown a centraliser segment 1 comprising a first collar portion 3, a second collar portion 5, bows 7 extending between the first and second collar portions 3 and 5, first connectors 9 and second connectors 11.

[0039] Two or more centraliser segments 1 may be connected together via the first and second connectors 9 and 11, as will be further described herein.

[0040] A first connector 9 is provided on the first collar portion 3 and on the second collar portion 5.

[0041] The first connectors 9 are provided on a first face 10 of the centraliser segment 1.

[0042] Each first connector 9 is provided as a series of teeth 13. The teeth 13 of the first connectors 9 extend on the first collar portions 3 and 5, respectively, from respective first ends 15 thereof. The series of teeth 13 terminate before the location at which a bow 7 extends between the first and second collar portions 3 and 5.

[0043] Each second connector 11 is provided as a guide 24 and a series of pawls 19 adjacent respective second ends 21 of the collar portions 3 and 5. Each guide 24 consists of a series of L-shaped lugs 24A extending on each side of the pawls 19 in an opposed manner.

[0044] The second connectors 11 are provided on a second face 17 of the centraliser segment 1.

[0045] The teeth 13 and pawls 19 of the first and second connectors 9 and 11, respectively, form a pawl and ratchet connection arrangement. This allows the relative positional engagement between the first and second connectors 9 and 11 to be selected as will be further described later herein.

[0046] The first and second collar portions 3 and 5 are provided as strap-like members and are substantially parallel to one another.

[0047] The bows 7 extend between the first and second collar portions 3 and 5 intermediate the locations of the first and second connectors 9 and 11 on the first and second collar portions 3 and 5.

[0048] The bows 7 have an inbuilt curvature in their longitudinal direction, in which they extend, between the first and second collar portions 3 and 5. This can be best seen in FIGS. 5 and 7.

[0049] The bows 7 are strap-like members.

[0050] The bows 7 are flexibly resilient.

[0051] The bows 7 are provided with rib members 22 on the first face 10 of the centraliser segment 1 that, in use, faces the borehole casing. The rib members 22 extend diagonally across the width of the bows 7 for substantially the length of the bows 7.

[0052] The rib members 22 are each provided with an enlarged portion 22 a. The enlarged portion 22 a is provided midway along the length of each rib member 22.

[0053] A pair of lugs 23 is provided on each of the first and second collar portions 3 and 5. The lugs 23 are provided on the second face 17 of the centraliser segment 1 that, in use, faces away from the borehole casing. One of the lugs 23 on each collar portion 3 and 5 is located adjacent the respective first ends 15 of the collar portions 3 and 5. The other lug 23 on each collar portion 3 and 5 is located approximately midway along the length of the respective collar portions 3 and 5.

[0054] Slots 25 are provided in the collars 3 and 5. The slots 3 and 6 increase the flexibility of the collars 3 and 5 and save on the raw material from which the centraliser segment 1 is made. However, the slots 25 may, alternatively, be omitted.

[0055] The centraliser segment 1 is made of a corrosion resistant material.

[0056] The manner of operation and use of the centraliser segment 1 of the present invention will now be described.

[0057] Two or more centraliser segments 1 are able to be connected together via the first and second connectors 9 and 11 to form a centraliser 30 shown in FIGS. 9 and 10. In FIGS. 9 and 10, the centraliser 30 is formed of two centraliser segments 1 a and 1 b, respectively, connected together around a borehole casing 100, This is done by inserting the ends 15 of the first and second collar portions 3 and 5 of the first centraliser segment 1 a beneath and between the opposed L-shaped lugs 24A of the guides 24 of the second connectors 11 of the second centraliser segment 1 b. This causes the teeth 13 of the first connectors 9 of the first centraliser segment 1 a to engage with the pawls 19 of the second connectors 11 of the second centraliser segment 1 b. Similarly, the ends 15 of the first and second collar portions 3 and 5 of the second centraliser segment 1 b are inserted beneath and between the opposed L-shaped lugs 24A of the guides 24 of the second connectors 11 of the first centraliser segment 1 a. This causes the teeth 13 of the first connectors 9 of the second centraliser segment 1 b to engage with the pawls 19 of the second connectors 11 of the first centraliser segment 1 a. The above described procedure is carried out with the centraliser segments 1 a and 1 b positioned around the borehole casing 100.

[0058] The teeth 13 of the first connectors 9 of the first centraliser segment 1 a engage with pawls 19 of the second connectors 11 of the second centraliser segment 1 b. This can be seen in FIG. 9, Similarly, the teeth 13 of the first connectors 9 of the second centraliser segment 1 b engage with pawls 19 of the second connectors 11 of the first segment 1 a. This, however, is obscured in FIG. 9 by the borehole casing 100.

[0059] The connections between the first and second centraliser segments 1 a and 1 b can be adjusted by using a tool, such as a pair of pliers, to grip the lugs 23 a adjacent the ends 15 of the first centraliser segment 1 a and the lugs 23 b located midway along the length of the collar portions 3 and 5 of the second centraliser segment 1 b to thereby pull the collar portions 3 a and 5 a of the first centraliser segment 1 a further through the guides 24 b of the collar portions 3 b and 5 b of the second centraliser segment 1 b. In this way, the first and second centraliser segments 1 a and 1 b, that form the centraliser 30, can be tightened around the borehole casing 100.

[0060] The ability to pull the collar portions 3 and 5 of one centraliser segment 1 through the guides 24 of another centraliser segment 1 until the centraliser 30 is tightly affixed around the borehole casing 100 means that the relative positional engagement between the first and second connectors 9 and 11 can be selected to achieve the required tightness. Additionally, it means that a centraliser, whether made up of one or more centraliser segments according to the present invention, can be adjusted to fit a range of borehole casings 100 of differing diameters.

[0061] If the borehole casing 100 is of a large diameter such that it cannot be surrounded by a pair of centraliser segments 1, then three or more centraliser segments may be connected together via the first and second connectors 9 and 11 around the borehole casing 100.

[0062] A centraliser 30 is fixed around a borehole casing 100 prior to the borehole casing 100 being inserted into a borehole 102. A borehole casing 100 is generally made by connecting casing lengths together as the borehole casing 100 is inserted deeper into the borehole 100. Typically, these casing lengths may be six or nine meters in length. A centraliser 30 may be provided every few meters along the length of the borehole casing 100.

[0063] The amount of curvature in the bows 7 of the centraliser segments 1 forming a centraliser 30 can be varied to accommodate the clearance in the borehole 102 into which the borehole casing 100 is being inserted. This is done by first affixing one collar of the centraliser 30 around the borehole casing 100. Using the centraliser 30 in FIG. 9 as an example, the collar portions 5 a and 5 b of the first and second centraliser segments 1 a and 1 b may first be tightly affixed together around the borehole casing 100 to form a first collar of the centraliser 30. If an increased curvature in the bows 7 is required, then the collar portions 3 a and 3 b are pushed downwardly along the borehole casing 100, in the direction of arrow A, before they are firmly affixed around the borehole casing 100. Pushing the collar portions 3 a and 3 b in the direction of arrow A, towards the collar portions 5 a and 5 b, will increase the curvature of the bows 7. Pulling the collar portions 3 a and 3 b upwardly, in the direction of arrow B will lessen the curvature of the bows 7.

[0064]FIG. 10 shows a borehole casing 100 in position in a borehole 102 with a centraliser 30 affixed around the borehole casing 100. The bows 7 of the centraliser segments 1 which form the centraliser 30 contact the wall 104 of the borehole 102.

[0065] Due to the bows 7 being flexibly resilient, as the borehole casing 100 is pushed into the borehole 102, the bows 7 deform if they encounter any obstruction in the wall 104 of the borehole 102. Furthermore, once the bows 7 pass over the obstruction, they will return to their normal undeformed position to maintain contact with the wall 104 of the casing 100.

[0066] Maintaining the bows 7 in contact with the wall 104 of the borehole 102 ensures that the borehole casing 100 remains centralised as it is pushed further down into the borehole 102.

[0067] The enlarged portions 22 a of the rib members 22 ensure that, in the event of a collapse of the wall 104, a minimum clearance is retained between the bows 7 and the borehole casing 100. This minimum clearance is determined by the thickness of the enlarged portions 22 a.

[0068] Once the borehole casing 100 is in position in the borehole 102, a grout discharge pipe can be lowered down the borehole casing 100. Grout is then discharged from the opening of the grout discharge pipe so that it flows into the annular space between the borehole pipe 100 and the wall 104 of the borehole 102. The grout then Rows upwardly in the annular space and fills the annular space with grout as shown by reference numeral 106.

[0069] The ribs 22 of the centraliser segments 1 promote agitation of the grout as it flows upwardly in the annular space around the centralisers 30. Such agitation assists in achieving an even grout filling of the annular space without channels and cavities.

[0070] Once the grout 106 has set, the borehole casing 100 remains centralised in the borehole 102 and can be used for its intended purpose.

[0071] The centraliser according to the second embodiment of the present invention is used in a similar manner to the centraliser according to the first embodiment of the present invention, except that the centraliser of the second embodiment is used with borehole casings having a relatively small diameter such that only a single centraliser segment is used to form the centraliser around the borehole casing. Accordingly, in the second embodiment of the centraliser, the centraliser segment used has its first connector 9 on the first collar portion 3 connected to the second connector 11 on the first collar portion 3 and the first connector 9 on the second collar portion 5 is connected to the second connector 11 on the second collar portion 5.

[0072] In addition, if required, two or more centraliser segments that are used to form a centraliser according to the second embodiment may be connected together around a borehole casing to form a centraliser in similar manner to the centraliser segment 1 that is used to form a centraliser according to the first embodiment of the present invention, However, the centraliser segment 1 intended to form a centraliser for medium to large diameter borehole casings, would usually be too large to be used to form a centraliser formed of only a single centraliser segment on a small diameter borehole casing

[0073] Modifications and variations such as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

[0074] Throughout the specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. 

I claim:
 1. Centraliser segment comprising a first collar portion, a second collar portion, bow means extending between said first collar portion and said second collar portion, first connection means provided at first locations of said first collar portion and said second collar portion, respectively, second connection means provided at second locations of said first collar portion and said second collar portion, respectively, wherein said first connection means are engagable with said second connection means of the same or another centraliser segment such that one or more centraliser segments are connectable together to form a centraliser around a borehole casing.
 2. Centraliser segment according to claim 1 , wherein said first and second connection means allow the relative positional engagement between said first and second connection means to be selected.
 3. Centraliser segment according to claim 1 , wherein said first connection means comprises teeth provided on said first and second collar portions on a first face of said centraliser segment and said second connection means comprises pawl means provided on said first and second collar portions on a second face of said centraliser segment.
 4. Centraliser segment according to claim 1 , wherein said second connection means further comprises guide means for receiving first and second collar portions of a said centraliser segment.
 5. Centraliser segment according to claim 1 , wherein said first and second collar portions are provided with lug members on a face of said centraliser segment that in use, faces away from the borehole casing.
 6. Centraliser segment according to claim 1 , wherein said bow means is flexibly resilient.
 7. Centraliser segment according to claim 1 , wherein said bow means is curved in the direction between said first and second collar portions.
 8. Centraliser segment according to claim 1 , wherein said bow means extends between said first and second collar portions intermediate the locations of said first and second connection means.
 9. Centraliser segment according to claim 1 , wherein agitation promoting means is provided on said centraliser segment to promote agitation of grout injected into a borehole.
 10. Centraliser segment according to claim 9 , wherein said agitation promoting means comprise rib members provided on said bow means.
 11. Centraliser segment according to claim 10 , wherein said rib members are provided on a face of said centraliser segment that, in use, faces the borehole casing.
 12. Centraliser segment according to claim 10 , wherein at least one of said rib members is provided with at least one enlarged portion.
 13. Centraliser segment according to claim 1 wherein said bow means comprises at least two strap members extending between said first and second collar portions.
 14. Centraliser segment according to claim 1 , wherein said first and second collar portions are substantially parallel.
 15. Centraliser segment according to claim 1 , wherein said first and second collar portions are provided as strap members.
 16. Centraliser segment according to claim 1 , wherein said centraliser segment is made of a corrosion resistant material.
 17. Centraliser for a borehole casing comprising a centraliser segment according to claim 1 , connected together via said first and second connection means around a borehole casing.
 18. Centraliser according to claim 17 , wherein said centraliser comprises at least two centraliser segments connected together via said first and second connection means around a borehole casing.
 19. Centraliser for a borehole casing comprising at least two centraliser segments according to claim 1 connected together via said first and second connection means around a borehole casing. 